Balance wheel motion limiter



Sept. 13, 1955 F. KOEHLER BALANCE WHEEL MOTION LIMITER Filed June 2, 1954 IFIG.3

INVENTOR FRED KOEHLER ATTORNEY United States Patent BALANCE WHEEL MOTION LIMITER Fred Koehler, Lancaster, Pa., assignor to Hamilton Watch Company, Lancaster, Pa.

Application June 2, 1954, Serial No. 433,895

2 Claims. (Cl. 58-107) This invention relates to a means for preventing the balance wheel from passing through more than 297 in one direction in a single oscillation.

In the type of Watch such as the electromagnetic watch, where the balance wheel is driven directly from the source of power and itself drives the train to move the hands, there is no roller or pallet fork to prevent the balance wheel under shock from making more than a complete revolution in one direction. In the type of watch such as the electromagnetic watch, this would result in additional contact making with the result that the watch would run twice as fast as it should run. It is, therefore, necessary to provide a stop or other limiting factor to prevent the balance wheel from turning through 360 in one direction in any one oscillation.

The object of the present invention is to provide means carried by the balance wheel which will limit the motion of the balance Wheel to less than 360 in any one direction for any one oscillation.

It is a still further object of the present invention to provide means on the balance arm for engaging the outside coil of the expanded hairspring and to limit the motion of the balance wheel through that engagement to an arc of less than 360 in one direction in any one oscillation.

A further object of the present invention is to provide means carried by the balance wheel for engaging the hairspring during the rotation of the balance wheel in one direction through an arc of from 270 to 360 and limiting the motion of said balance wheel in the one direction for one oscillation to that arc, and at the same time prevent the possibility of entangling the hairspring with any portion of the engaging means.

A further object of the present invention is to provide a pin on the balance arm of the balance wheel for engaging the outer coil of the expanded hairspring at approximately 297 of arc of the balance wheel from a point of rest in one direction and during one oscillation.

The invention is illustrated in the accompanying drawings in which:

Figure 1 is a top plan view of a portion of the balance wheel and hairspring with the limiting stop shown in the rest position and the hairspring engaging position.

Figure 2 is a cross section showing the hairspring at point of engagement with the limiting pin.

Figure 3 is a similar view setting forth the use of the slope for returning the hairspring to normal position.

Referring particularly to the drawings, a balance wheel having a cross arm 8 has its upper pivot support in the balance cock 9 in the usual manner. A conventional regulator arm 10 carries the regulating pins 11 for adjusting the period of the hairspring which is held to the balance cock by the stud 12.

The hairspring 13 is secured to the balance statI by the collet 13' and is shown in Figure 1 at the point of rest of the balance wheel in solid lines and at the point of "ice greatest expansion in dotted lines. Mounted on the balance wheel arm 8 is a pin 14 bent at 15 to provide a sloping portion 16 extending downward to contact the balance arm at 17. The end 17 of the pin is beveled to make a flat contact with the surface of the balance arm to relieve the pin of any possible projections upon which the hairspring might be caught.

In the operation of the device the balance wheel rotates approximately a turn and a half or through 270 of arc from a point of rest in one direction during any one oscillation. To turn further than this might result in turning through more than 360 of arc and cause overswinging, which is referred to in a spring wound watch as overbanking. With a watch of the spring type, this overbanking is prevented by the engagement of the jewel pin with the pallet fork, but in a watch of the electromagnetic type where there is no pallet fork and no jewel pin the turning of the balance wheel through more than 360 of arc will result in an additional contact and an additional impulse to the wheel. This overswinging is generally brought about by a shock or sudden movement of the person carrying the wrist watch, and some means for preventing the balance wheel from turning through more than 360 of arc in one direction in any one oscillation must be provided.

Upon movement of the balance arm through 297, the upstanding pin 14 engages the outermost expanded coil of the hairspring and brings the balance wheel to a comparative slow stop. It is possible that a shock to the watch would cause the outermost coil of the hairspring to override the pin 14 as shown in Figure 3, whereupon the sloping surface 16 will return the outermost coil of the hairspring to normal position upon the return motion of the balance wheel, the end 17 fitting closely against the surface of the arm 8 leaving no projection for the coil of the hairspring to engage and to hang up on.

What is claimed is:

1. In a watch of the electromagnetic type having a balance wheel driven directly by a source of motive power, a hairspring connected to and expanding and contracting with the motion of said balance wheel, a pin carried on the cross arm of said balance wheel and adapted to engage the expanded outside spiral of the hairspring upon movement of the balance wheel through more than 297, and means integral with said pin for guiding said expanded outside spiral of the hairspring back to its original position should said hairspring override said pin.

2. In a watch of the electromagnetic type having a balance wheel driven directly by a source of motive power, a hairspring connected to and expanding and contracting with the motion of said balance wheel, a pin carried on the cross arm of said balance wheel, said pin extending at right angles from said balance wheel in a vertical position for a portion of its length and the remainder of its length being bent over and directed at an angle back toward said cross arm to form an angled guard sloping from the top of the pin away from the center of the balance wheel to guide the outermost coils of the hairspring back to their original positions should they override the uppermost point of said pin.

References Cited in the tile of this patent UNITED STATES PATENTS 1,911,062 Conrad May 23, 1933 2.60l,l74 Smith June 17, 1952 FOREIGN PATENTS 28,540 Switzerland July 17, 1908 

